Circuit board includes conductive blind holes. The conductive blind hole electrically connects at least two conductive circuit layers. The conductive blind hole is formed by drilling hole, and then plating conductive metal in the hole. A circuit board having a conductive blind hole with a big ratio of hole depth to hole diameter can be designed for dense line with high reliability. Thus, a new circuit board in which the conductive blind hole with a big ratio of hole depth to hole diameter is preferred.